sciencetech-blog

comments

Evidence for a giant glacier that once existed in the deepest canyon on Mars has been found.

A type of mineral 1.2 miles (2km) up the side of the canyon wall suggests that a huge glacier once passed through - potentially carving out the shape we see today.

While the idea of a glacier is controversial, the scientists say such a theory is the best explanation for their latest findings.

Research led by Dr Selby Cull from Bryn Mawr College in Philadelphia suggests that part of Valles Marineris may have been formed by a glacier. Evidence comes from a mineral called jarosite found half way up the cliff wall (shown), which may have been the top of an ancient glacier that has long since disappeared

The research was led by Dr Selby Cull from the Department of Geology at Bryn Mawr College in Philadelphia.

Evidence for the glacier comes in the form of the mineral jarosite being spotted in the wall, a sulphate that forms in highly acidic water with low temperatures - such as the top of a glacier on Mars.

While evidence for glaciers on Mars has been spotted before, this is one of the first times evidence for one has been found in Valles Marineris.

Dr Cull tells MailOnline the best explanation for the discovery of jarosite here is that a glacier once filled half the canyon.

The jarosite was found in a thin layer 330ft (100 metres) along part of the cliff wall, suggesting it was once the boundary of the top of an ancient glacier.

'The canyon wall starts at about zero metres elevation and descends to about -4,000 metres [2.5 miles],' she explains.

'We see the jarosite at -1,900 to -2,000 metres [1.18 to 1.24 miles], so about half-way down the canyon wall.'

She continued: 'We found [jarosite] in a few places on Mars before, but the exciting thing here is we found it half way up a 3-mile [4.8km] high cliff face in the North Marineris.

'All previous jarosite deposits have been found in low-lying deposit areas, places where water would cool.'

Jarosite usually forms in wet and acidic locations like rivers and groundwater, but Dr Cull explains that couldn't have happened here.

'It would have required half the valley to be filled with water, which would have left huge indicators and evidence that there had been water there, and there's no evidence,' she says.

'So we think the only viable way you see jarosite is if there was a glacier.'

If true, this would be among the first mineralogical evidence for glaciers in the Ius Chasma - one of the largest portions of Valles Marineris.

The mineral known as jarosite must have been desposited by highly acidic water at low temperature - and a glacier is the best explanation. Dr Cull says it could not have been a regular water flow such as a river as it would have had to fill half the deep canyon (Ius Chasma shown in image)

The discovery was made using instruments on Nasa's Mars Reconnaissance Orbiter (left) and Esa's Mars Express (right) spacecraft. Further observations in future will be used to verify the findings

Dr Cull admits the theory that this canyon was formed by a glacier remains controversial in the scientific community.

But she says other explanations for this feature just don't make sense.

One possibility was that this jarosite came from a water table but, as it is not near the surface, Dr Cull says this would require the water table to be slanted, 'which is a very strange thing for a water table to do.'

The team used data from two spacecraft, Nasa's Mars Reconnaissance Orbiter and Esa's Mars Express, to make the findings.

'If it was a glacier, it would be the top point of the glacier,' Dr Cull continues.

The mineral jarosite would form at the top of the glacier, where the ice melts, and be deposited on the cliff wall.

One other theory is that this jarosite was deposited by an acid fog.

Acid fog is essentially water vapour that is highly enriched in sulphur, which can be released during volcanic emissions.

However, with no volcanic vents nearby, this theory looks unlikely.

'We are continuing to map Ius Chasma, and will map the surrounding wall surfaces to see if we can find this same mineral elsewhere,' Dr Cull adds. 'It's very exciting.'

Named after the Mariner 9 Mars orbiter of 1971/1972, Valles Marineris is one of the largest systems of canyons in the solar system. It is located on the Martian equator and stretches for a quarter of the planet's circumference. This image of Valles Marineris was taken by Nasa's Viking orbiter in June 1992